> Also, if there is no closed circuit, how/why are the
> electrons accelerating? Even if there is a potential
> difference of 12 V, there is no conductor in between
> for them to move in?

Once it leaves the antenna, it can be helpful to think of radio waves like
light.  In fact, they basically are light; low frequency light.  And the
lower the frequency, the less like light.

At frequencies above about 100 MHz, propagation is pretty much line of
sight, just like light.  At frequencies above about 1 GHz or so, things
like rain and fog interfere with the propagation, much like light.

As you get lower, funny things happen.  In the tens of megahertz range,
the waves sometimes "bounce off" the ionosphere, which is why short wave
propagation works over huge distances.  The waves are still pretty much
line of sight, it's just that there is a huge mirror in the sky.  At still
lower frequencies, there is a tendency to follow the earth's curvature. 
This is why you can hear a powerful AM station well beyond line of sight.

Someone earlier in this thread said something along the lines of anyone
who thinks he knows all about radio is fooling himself. This is pretty
much true.  But it isn't too hard to understand enough to use it
effectively, and only a little harder to learn enough to design circuits.

A lot of people mentioned the ARRL Handbook, which has become pretty much
the bible for these things.  The Handbook is published every year, and it
doesn't change a lot from year to year.  For your initial studies, a copy
10 or even 20 years old will be good enough for your purposes, and these
can be found at flea markets or online for far less than the latest copy. 
On the other hand, it isn't all THAT expensive new, and an online order
direct from the ARRL or any of dozens of other outlets could be quick and
easy.

--McD


-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist